Generally, energy E of a film capacitor is represented by the equation (1):E=(½)CV2=(½)∈(S/d)V2  (1)wherein C represents a capacity of a capacitor, and ∈ represents a dielectric constant, S represents a surface area of a film, d represents a film thickness and V represents a withstanding voltage. Therefore, in order to increase energy of a film for a film capacitor, increase in dielectric constant and withstanding voltage and decrease in film thickness are demanded.
So far, the use of vinylidene fluoride (PVdF) has been proposed for a film for a film capacitor from the viewpoint of its high dielectric constant (for example, cf. JP56-162822A).
Also, there is disclosed a method of producing a film for a film capacitor by a coating method since it is easy to make a film thin (for example, cf. JP60-40137A and JP59-62115A). On the other hand, there is disclosed a method of using a copolymer comprising vinylidene fluoride (VdF), ethylene and tetrafluoroethylene (TFE) (for example, cf. JP59-226409A and JP59-230208A).
As mentioned above, various proposals have been made, but a thinner film having both of a higher dielectric constant and a higher withstanding voltage is desired.